Categories: Gamma Ray Bursts

The Gamow Explorer Would be a new Gamma-ray Observatory to Search for the First Stars in the Universe… as They Explode

Gamma rays are useful for more than just turning unassuming scientists into green-skinned behemoths.  They can also shine a light on the deaths of some of the earliest stars in the universe.  More accurately, they are some of the light caused by the deaths of the earliest stars in the universe.  Now, a team of scientists led by Nicholas White of George Washington University, and formerly of NASA’s Goddard Space Flight Center, has proposed an observatory mission that would scan the sky for evidence of Gamma-ray bursts (GRBs) and use them to understand the early universe.

The mission is currently named the Gamow Explorer after George Gamow, one of the originators of the Big Bang theory (the scientific theory – not the popular American TV show).   It will peer into a period of the early universe called the Epoch of Reionization, where the hydrogen that made up the early universe went from being neutral to its ionized form.  To do so, Gamow will look at GRBs, the most luminous explosions in the universe.

GRBs are so fantastic, they warrant their own UT video!

Mission designers have put forward a three-step concept to catch and fully characterize GRBs as they happen.  First, Gamow will frequently use the Lobster Eye X-ray Telescope (LEXT) to scan the sky for GRBs.  Lobster-eye optics have the added advantage of capturing a large portion of the sky all at once. They were originally proposed back in the 70s by J. Roger P. Angel, now at the University of Arizona, more recent technological advances have made the wide field of view inherent to lobster-eye optics easier to achieve technologically.

Those technological advances help in another crucial area of GRB analysis – speed.  GRBs evolve rapidly, with even “long duration” bursts lasting on average less than 30 seconds.  While the LEXT is good at initially detecting the GRBs, it’s not so good at collecting the detailed spectral data the scientists require.  That is where the second Gamow instrument comes in – the Photo-z Infra-Red Telescope (PIRT) is designed to react to data from LEXT and turn toward any ongoing GRB.  

Depiction of the electromagnetic radiation from a GRB.
Credit – White et al.

Initially proposed in a paper earlier this year, the PIRT concentrates on collecting data necessary to find GRBs that are exceptionally far away.  To catch these fleeting explosions, Gamow is designed to turn the PIRT toward any potential GRB candidate found by LEXT within 100 seconds of its discovery.

While PIRT captures the infrared wavelength data of the GRBs afterglow, Gamow itself will be busy coordinating with a series of connected satellites in an attempt to turn as much observational power as possible towards the GRB.  Within 1000 seconds of discovering a new GRB, the mission is designed to inform other powerful telescopes.  These helping hands could include the soon-to-be-launched James Webb Space Telescope (JWST) and other ground-based telescopes that peer into the radio and visible light spectra.  

A THESEUS SXI model that was a design inspiration for Gamow’s LEXT module.
Credit – Feldman et al.

Part of the long delay in bringing other systems to bear on a GRB would be caused by Gamow’s location.  Mission planners envision the telescope at the L2 Lagrange point, the same location as the JWST.  But even at that distance, the radio telescopes on Earth would be able to see some of the afterglow that had first been discovered by the BeppoSAX observatory and confirmed by the Neil Gehrels Swift Observatory. Gamow would dwarf these two predecessor missions in both capability and sensitivity.  

All that horsepower is great, but what is it good for?  The GRBs that Gamow is searching for are most likely caused by the merger of extraordinarily dense objects – the exact kind of impacts that are thought to cause gravitational waves.  So far, linking the electromagnetic output of such events to the gravitational waves caused by them has proved tricky.  Gamow’s speedy response time is a straightforward solution to that problem, which has plagued the astronomy community ever since the confirmation of gravitational waves themselves in 2017.  

CAD model of the LEXT’s focal plane.
Credit – Feldman et al.

There’s still a long way to go before Gamow or a similar would get off the ground, though.  The mission team plans to propose the concept as part of NASA’s 2021 MIDEX call, designed for “medium” sized missions, the likes of which were recently endorsed by the Decadal Survey.  But proposals are not guaranteed funding, though a similar idea, known at the Transient Astrophysics Observatory, has been floating around the astronomical community for at least four years.

If accepted into the MIDEX program, Gamow plans to lift off in 2028 and start collecting data on some of the most brilliant explosions in the galaxy soon after that.  Even then, though, it won’t be transforming any of its mission scientists into a superhero.

Learn More:
arXiv – The Gamow Explorer: A gamma-ray burst observatory to study the high redshift universe and enable multi-messenger astrophysics
NASA – The Gamow Explorer
arXiv – LEXT: a lobster eye optic for Gamow
NASA – Proposed NASA Mission Employs “Lobster-Eye” Optics to Locate Source of Cosmic Ripples

Lead Image:
CAD image of the Gamow explorer.
Credit – White et al.

Andy Tomaswick

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